Coated, antimicrobial, chemically strengthened glass and method of making

ABSTRACT

The disclosure is directed to a chemically strengthened glass having antimicrobial properties and to a method of making such glass. In particular, the disclosure is directed to a chemically strengthened glass with antimicrobial properties and with a low surface energy coating on the glass that does not interfere with the antimicrobial properties of the glass. The antimicrobial has an Ag ion concentration on the surface in the range of greater than zero to 0.047 μg/cm 2 . The glass has particular applications as antimicrobial shelving, table tops and other applications in hospitals, laboratories and other institutions handling biological substances, where color in the glass is not a consideration.

PRIORITY

This application claims benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application Ser. No. 61/371,364 titled “Functionally Coated Antibacterial, Chemically Strengthened Glass and Method of Making” filed Aug. 6, 2010 and U.S. Provisional Application No. 61/510,245 “Functionally Coated, Antimicrobial, Chemically Strengthened Glass and Method of Making” filed Jul. 21, 2011 the content of which is relied upon and incorporated herein by reference in its entirety.

FIELD

The disclosure is directed to a chemically strengthened glass having antimicrobial properties and method of making such glass. In particular, the disclosure is directed to a colorless transparent chemically strengthened glass with antimicrobial properties and with a functional coating on the glass that does not interfere with the antimicrobial properties of the glass.

BACKGROUND

The “health properties” of metallic silver (that is, its antiseptic, antibacterial, antiviral, antimicrobial effects) was known for centuries before knowledge of bacteria, viruses and microbes generally even existed. In antiquity (Hippocrates of Cos and Galen of Pergamum, both physicians), and well through the Middle Ages, silver vessels were used in the care of those who were ill and wounded. For example, E. Bradford in “The Great Siege [Malta, 1565]” (New York, Harcourt, Brace & World Inc., 1961, pp. 190-191) describes the practices of the Knights of the Order of St. John, who were hospitalers, at Malta as:

-   -   “Simple though their surgery was and ignorant though they were         in many ways, they did at least understand the rudiments of         hygiene. In the hospital, where under normal conditions both         rich and poor, Knight and commoner, were served off silver         plate—to increase “the decorum of the hospital and the         cleanliness of the sick”—some attempt was made, even during the         siege, to look after the patients properly.” [Emphasis added.         Internal quotation from Francisco Balbi de Correggio, “La         verdadera relación de todo to que el ano de MDLXV ha succedido         en la Isla de Malta,” (Barcelona, 1568)].

It was later discovered that the actual bactericide was not the metallic silver, but the silver ions on the surface of the bulk metallic silver. Thus, the beneficial effect of using silver vessels may be attributable to the migration of silver ions from the bulk silver to the food and drink that was consumed. With the knowledge that silver ions were are actual “antiseptic,” solutions of certain silver salts (e.g. silver nitrate) that are readily soluble in water were used as an antiseptic and bactericide for many decades. Until the 1980s, dilute silver nitrate eye drops were placed in the eyes of newborns to prevent neonatal conjunctivitis, which could lead to blindness in the newborn, which may occur after birth. (This practice has generally been discontinued in favor of the use of erythromycin ointment).

Recently, the use both metallic silver particles and silver salts have been described in the patent and technical literature as a means for imparting antibacterial properties to a variety of materials such as yarns, fabrics, glass and other materials. Yahoo Lv et al. (Polymers for Advanced Technologies, Vol. 19 (1008), pages 1455-1460) have shown that silver) (Ag⁰) nano-particles coated on a glass slide have antibacterial/antiviral properties resulting from close attachment of the nano-particles with the bacterial cells. The principle activity of silver (0) particles is due to the production of silver ions within an aqueous matrix containing the bacteria. Di Nunzio et al in WO 2006/058906 describe prosthetic devices or implants having at least a surface layer or a part thereof (that is, an element of the prosthetic device or implant) made of a glass, glass-ceramic or ceramic material containing ions exchangeable with silver ions, and subjecting the device “to a silver ion containing aqueous solution ion-exchange process,” [id at the Abstract]. Di Nunzio et al., J. European Ceramic Society Vol. 24 (2004), pages 2935-2942, discuss bioactive glasses containing silver on their surface that were produced by ion-exchange from dilute silver nitrate melts. Verne et al, J. Material Science; Materials Medicine Vol. 20 (2009), pages 733-740, present test results of the surface doping of biocompatible glass that was described in WO 2006/058906. U.S. Pat. No. 7,232,777 describes yarns and fabrics having an antimicrobial silver particulate finish.

Silver ions do not possess a single mode of action. They interact with a wide range of molecular processes within microorganisms resulting in a range of effects from inhibition of growth and loss of infectivity to cell death (cytotoxicity). The mechanism depends on both the concentration of silver ions that are present and the sensitivity of the microbial species to the silver ions. Contact time, temperature, pH and the presence of free water all impact on both the rate and extent of antimicrobial activity. However, the spectrum of activity is very wide and the development of resistance relatively low, especially in clinical situations. Silver ions are known to be effective against some 650 types of bacteria.

The prevalence of “touch screens” in contemporary society gives rise to many surfaces that can harbor microbes, bacteria and viruses, and these microbes can be transferred from person to person. The present disclosure is directed to glass surfaces and to the application of the antimicrobial properties of silver ions to glasses such as the cover glasses used on many modern devices, for example, ATMs, touch screen computers, cellphones, electronic book readers, and similar devices.

SUMMARY

This disclosure is directed to a making a chemically strengthened glass having antimicrobial properties and to methods of making such glass. In one embodiment the disclosure is directed to a colorless transparent chemically strengthened glass with both antimicrobial properties and a functional coating on the glass that does not interfere with the properties of the glass. The functional coating is used to impart easy cleanability to the surface and is generally a hydrophobic coating. The task of creating a chemically strengthened glass having antimicrobial properties and having a functional coating on the glass is not straightforward due to the fact that there are numerous other required properties of the cover glass that must be maintained while trying to incorporate the antimicrobial property. It should also be understood that the interaction of the Ag-ion with the bacteria is restricted to the surface of the glass, so the pertinent characterization of the concentration needs to be expressed as per unit area. The reporting of the volume concentration at some interior point away from the surface, for example, >5 nm is of little consequence since the mobility of Ag⁺¹ at room temperature is negligible.

Another embodiment the disclosure is directed to a method of making a chemically strengthened glass having silver ions (Ag⁺¹) on the surface of the glass. There have been proposals to utilize a one-step (1-step) method in which an ion-exchange bath containing both a silver compound and an ion-exchanging alkali metal compound whose ions are larger than the alkali metal ions in the article into which they be exchanged, and using such bath exchange both Ag ions and the larger ions into the glass in a single step to form a chemically strengthened, silver containing glass having a compressive stress. For example, in addition to the silver ions, the alkali metal ions that are exchanged into the glass are potassium ions (K⁺¹). Prior art and our experiments show that the 1-step ion-exchanging bath consisting of potassium nitrate containing silver nitrate in an amount in the range of 0.01 wt % to 5 wt % where the ion exchange temperatures are typically at 300-500° C. with ion exchange times of >3 hours exhibits distinct disadvantages. The most significant disadvantage is that to enhance the “kill” rate of bacteria and other microbes it is necessary that there be a sufficiently a high concentration of Ag-ion on the surface which is not achieved through the use a one-step process; and further when the 1-step method is used significant color is produced as a consequence. This color makes the glass unsuitable for use in electronic devices by altering the display, for example, by making it less clear or altering the colors.

Disclosed herein is a two-step (2-step) method that avoids the disadvantages of the 1-step method. The 2-step method uses a first ion-exchange bath containing an ion-exchanging alkali metal compound whose ions are larger than the alkali metal ions in the article into which they will be exchanged (the standard strengthening method on chemical strengthening), followed by ion-exchange using a second ion-exchange bath containing silver, the second silver-containing ion-exchange bath being used for a much shorter time than the first bath. The second ion-exchange bath contains a high concentration of both silver ions and an ion-exchanging alkali metal compound whose ions are larger than the alkali metal ions in the article into which they be exchanged, the silver ion concentration in the second bath being higher than that used in the in the silver-containing bath of the 1-step method. In the first step, the larger alkali metal ions are exchanged into the glass to form a glass article having a compressive stress in the usual manner for a time greater than 3 hours at a temperature in the range of 300-500° C.; for example, by ion-exchange at 420° C. for 5-6 hours. In the second step, the higher concentration of silver ions are exchanged into the surface of the glass and replace the alkali metal ions in the glass to a shallow enough depth without significant loss of compressive stress. In one embodiment of the 2-step method, the same alkali metal compound can be used in both the first and second ion-exchange baths. In certain embodiments of the 2-step method the silver compound and alkali metal compound used in the ion-exchange bath are both comprised of nitrates. Furthermore, the potassium ions are typically ion-exchanged for sodium and lithium alkali metal ions in the glass.

Generally, the 2-step method comprises providing a glass article containing ion-exchangeable alkali metal ions, providing a first ion-exchange bath containing ion-exchanging alkali metal compound whose ions are larger than the alkali metal ions in the article, and, as a first step, ion-exchanging the alkali metal ions in the glass for the alkali metal ions in the ion-exchange bath. As a second step, the method further comprises providing a second ion-exchange bath containing silver nitrate in an amount in the range of 1-10 wt %, the remainder of the bath being the nitrate of the an alkali metal ion having ion larger than the alkali metal ions at least equal in size to the alkali metal ions of the first ion-exchange bath. In one embodiment, the duration of the second bath exposure, that is, the ion-exchange time using the second bath, is less than 30 minutes in order to produce a shallow depth of exchange of less than 20 μm. In another embodiment the ion-exchange time is greater than zero and less than or equal to 20 minutes. In an additional embodiment, the ion-exchange time is greater than zero and less than or equal to 10 minutes. In all embodiments, the ion-exchange is carried out at a temperature in the range of 370° C. to 450° C. using a selected ion exchange time as described herein. In one embodiment, the ion exchange is carried out at a temperature in the range of 400° C. to 440° C. using a selected ion exchange time as described herein. The distinct advantage of the 2-step method is that since only the surface concentration of Ag⁺¹ is important for the antimicrobial effect, having the silver penetrate to greater depths as is achieved through the 1-step method adds nothing to the antimicrobial or antibacterial effect since silver ions do not move or migrate within the glass at temperatures at which electronic devices may be used; temperatures which typically range from below 0° C. to as high as 45° C. or higher. The 2-step method thus allows one to obtain a significantly higher concentration of Ag⁺¹ ions on the surface of the glass which results in a commensurate decrease in the “kill” time (the time to reach a log 3 reduction) while not producing any undesirable yellow color and therefore achieving the desirable transmittance characteristics as is shown in FIG. 1.

FIG. 1 compares the transmission in the 400-750 nm range of an antimicrobial glass ion-exchanged for 20 minutes using the 2-step method with an antimicrobial glass prepared by the 1-step method using the same ion-exchange bath for 5 hours. The glass of the 2-step method has a transmission, uncorrected for reflection losses, of greater than 88% over the entire range whereas the glass prepared by the 1-step method is less than 88% in the range of 400 mm to approximately 560 nm and equal to or greater than 88% only in the range of approximately 560 nm to 750 nm.

As mentioned above, the 2-step method, by restricting the second step to very short times, <30 minutes, one can produce a high concentration of Ag⁺¹ on the surface without imparting any color. In fact the silver ion concentration on the surface is larger for the short IOX time of the 2-step method compared to the longer IOX time (typically 4-6 hours) of the 1-step method. The volume concentration of Ag ion in the first 5 nm of the glass can be determined using XPS (x-ray photoluminescence-spectroscopy. Tables 1 and 2 show the XPS results for the Ag ion concentration in the first 5 nm of the glass.

TABLE 1 1-step Ion-Exchange Sample No Ag concentration, Atomic % 1 1.85 2 1.55 3 1.86 4 1.94 average 1.80 95% uncertainty 0.28 All samples ion-exchanged using the 1-step method and a 5 wt % AgNO₃/95 wt % KNO₃ bath at 420° c. for 5.5 hours

TABLE 2 2-step Ion-Exchange Sample No Ag concentration, Atomic % 1 2.68 2 1.97 3 2.22 4 3.22 Average 2.52 95% uncertainty 0.90 All samples were ion-exchanged using the 2-step method and a second step 5 wt % AgNO₃/95 wt % KNO₃ bath at 420° c. for 20 minutes

A comparison of the Tables 1 and 2 shows that the glass prepared by the 2-step method, 20 minute IOX time for the second bath, has a 40% increase in the Ag ion concentration in the first 5 nm relative to the Ag ion concentration in the glass produced by the 1-step, single bath process, 5% AgNO₃/95% KNO₃ bath being used in both processes.

Another aspect the present disclosure is the ability to produce a glass that has an antimicrobial surface that is easily cleanable without the loss of the antimicrobial activity. A “low surface energy” coating is applied to the surface of the silver-containing, chemically strengthened antimicrobial glass to impart easy-to-clean properties to the glass surface. The low surface energy coating is a hydrophobic coating that facilitates the ease of cleanability of the surface. In one embodiment, the low surface energy coating has a thickness in the range of 0.5 nm to 20 nm. In another embodiment, the low surface energy coating is a continuous coating and has a thickness in the range of 0.5 nm to 10 nm. In a further embodiment, the film is continuous and has a thickness in the range of 0.5 nm to 5 nm. In an additional embodiment, the thickness is in the range of 1 nm to 5 m. In an additional embodiment, the film is continuous and has a thickness in the range of 1 nm to 5 nm. In another embodiment, the low surface energy coating can form a pattern or domains on the surface, for example without limitation, “islands-in-the-sea” where the silver-containing, chemically strengthened surface of the glass is the sea and the low surface energy coating forms the islands. Stated another way, the low surface energy coating is discontinuous and does not cover every portion of the glass surface, but does cover a sufficient portion of the surface such that the coating is effective for its intended antimicrobial use and for its use in facilitating ease of cleanability. Such discontinuous coating can also vary in thickness over the range of 0.5 nm to 20 nm. In one embodiment, the discontinuous coating has a thickness in the range of 0.5 nm to 10 nm. In an additional embodiment, the discontinuous coating has a thickness in the range of 1 nm to 5 nm. In a still further embodiment, the coating can be a continuous “peak-to-valley” (“PV”) coating where the coating “peak” is thicker than the coating “valley”. For example, within the range of 0.5 nm to 20 nm, the coating within the “peak” can be in the range of 15 nm to 20 nm and the coating within the “valley” areas can be, for example, in the range of 1 nm to 5 nm. The selected depth to which the Ag⁺¹ ions are deposited may vary according to the silver concentration in the IOX bath, the temperature of the bath and the time for which the ion-exchange of the silver ions into the glass was carried out.

In one embodiment, the surface of the glasses described herein having antimicrobial activity and exhibiting a surface Ag ion concentration of greater than zero to 0.05 μgAg/cm², are not cytotoxic. In another embodiment, the non-cytotoxic glass has a surface Ag ion concentration in the range of 0.005 μgAg/cm² to 0.047 μgAg/cm². In an addition embodiment the non-cytotoxic glass has a surface Ag ion concentration in the range of 0.005 μgAg/cm² to 0.035 μgAg/cm². In a further embodiment, the non-cytotoxic glass exhibits a surface concentration in the range of 0.01 μg/cm² to 0.030 μg/cm². In an additional embodiment the surface concentration of the non-cytotoxic glass is in the range of 0.015 μg/cm² to 0.03 μg/cm².

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of the optical transmission (not corrected for reflection losses) comparing the results from the 1-step process (5 wt % AgNO₃ in KNO₃, 5.5 hours, 420° C.) for incorporating Ag ions into a glass with the 2-step process (100 wt % KNO₃, 420° C., 5.5 hours, followed by 5 wt % AgNO₃ in KNO₃, 95 wt % KNO₃, 20 minutes, 420° C.) for Ag ion incorporation into a glass.

FIG. 2 is an SEM micrograph of the surface of a chemically strengthened, silver ion containing antimicrobial glass coated with a low surface energy coating, the micrograph showing the domains of the coating material as dots of varying size on the surface of the glass.

FIG. 3 is a schematic diagram of the modified JISZ 2801: 2000 method used for evaluating the antibacterial properties of silver-containing glass having a hydrophobic coating on their surface.

FIG. 4 is graph of EMP results showing the actual silver ion concentration, calculated Ag₂O, versus depth for glass samples that were prepared by the 2-step method using different concentrations of AgNO₃ in the second bath.

FIG. 5 is a graph of EPM results illustrating the decrease in Ag ion concentration as one proceeds from the center of the glass to the surface of the glass.

FIG. 6A is a graph illustrating Ag ion surface concentration in ions/cm²×10¹⁴ versus wt % Ag₂O.

FIG. 6B is a graph of a graph of the Ag surface concentration in μg/cm² versus the wt % Ag₂O.

FIG. 7 is a graph comparing the antimicrobial activity, as log reduction versus time, for a silver ion containing glass as prepared by the 2-step method using a second IOX bath containing 0.15 wt % Ag.

FIG. 8 is a graph of bacterial “kill” time versus surface Ag-ion concentration.

DETAILED DESCRIPTION

As used herein the term “antimicrobial,” means an agent or material, or a surface containing the agent or material that will kill or inhibit the growth of microbes from at least two of families consisting of bacteria, viruses and fungi. The term as used herein does not mean it will kill or inhibit the growth of all species microbes within such families, but that it will kill or inhibit the growth or one or more species of microbes from such families. The components of all the glass compositions suitable for ion-exchange are given in terms of weight percent (wt %) as the oxide unless indicated otherwise. The surface concentration of antimicrobial silver ions is given in μg/cm² and refers to the concentration on the surface of the glass, and not to silver ions “near” or “close to” the surface. Also herein the term “2-step method” includes not only the glass compositions recited herein, but also any glass composition, from any source, that is suitable for chemical strengthening by ion-exchange to impart a compressive stress to the glass, or any glass that may have been chemically strengthened for another purpose and is used to prepare an antimicrobial glass according to the second step of the 2-step method.

As used herein the term “Log Reduction” or “LR” means Log (Ca/C₀), where C_(a)=the colony form unit (CFU) number of the antimicrobial surface containing silver ions and C₀=the colony form unit (CFU of the control glass surface that does not contain silver ions. That is: LR=−Log(C _(a) /C ₀), As an example, a Log Reduction of 4=99.9% of the bacteria or virus killed and a Log Reduction of 6=99.999% of bacteria or virus killed.

As used herein the term “low surface energy coatings” are hydrophobic coatings, for example without limitation,

(a) (RO)_(4-z)—Si—[(CH₂)₃—OCF₂—CF₂—[OCF₂—CF₂—CF₂]_(n)—F]_(z), where z=1 or 2, n is an integer sufficient to provide that [(CH₂)₃—OCF₂—CF₂—[OCF₂—CF₂—CF₂]_(n)—F] has a length in the range of nm to 20 nm, and RO═CH₃O—, CH₃—CH₂O—, or CH₃C(O)O—, and

(b) (RO)_(4-z)—Si—[(CH₂)_(x)—(CF₂)_(y)—CF₃]_(z), where x+y are integers whose sum is sufficient to provide that [(CH₂)_(x)—(CF₂)_(y)—CF₃] has a length in the range of 1 nm to 20 nm, with the provision that y≧x, z is 1 or 2, and RO═CH₃O—, CH₃—CH₂O—, or CH₃C(O)O—.

The values of n, x and y in the above two formulas can be determined using the covalent radius of carbon and oxygen which are 0.077 nm and 0.073 nm, respectively. The coating has to have a sufficiently long spacer, for example, a plurality of —CH₂—, —CF₂—, —O—(CH₂ and/or CF₂)_(n) moieties, or combination or such moieties, between the Si atom and the terminal fluorocarbon group, for example, CF₃, so that water can contact the glass surface of the glass and transport silver ions from the glass to a microbe. In one embodiment, the total length of the spacer or skeletal chain from the silicon atom and the chain's terminal moiety, for example, CF₃, is in the range of 1-20 nm. In another embodiment, the total length is in the range of 2-10 nm. In another embodiment, the total length is in the range of 1-10 nm. The silane coating material is attached to the silver-containing glass's surface by 2 or 3 Si—O bonds.

The methods described herein can be used to make antimicrobial glass samples of any thickness. In one embodiment, for example, for use in electronic devices as a touch screen or a touch screen cover glass, for example without limitation, cell phones, computer (including laptops and slates) and ATMs, the glass typically has a thickness in the range of 0.2 mm to 3 mm. In one embodiment the glass has a thickness in the range of 0.2 mm to 2.0 mm. In a further embodiment, the glass has a thickness in the range of 0.3 mm to 0.7 mm. The exemplary glass samples described and used herein for testing were 0.5 mm thick unless specified otherwise. Other applications include use as table tops or cover top, shelving in refrigerators or for storage shelves or shelf cover in, for example, laboratories, hospitals and other facilities where antimicrobial properties are desired. It should be noted that the glass can be thicker according to the intended use. For example, for a hospital bench top or bench top cover, it may be desirable that the glass have a thickness of greater than 3 mm.

Any glass composition capable of being ion-exchanged can be used in accordance with this disclosure. Such glass compositions typically contain the smaller alkali metal ions, typically Na and Li ions that can be exchanged by larger alkali ions, for example by K, Rb and Cs ions and silver ions. In addition, any glass composition, from any source, that is suitable for chemical strengthening by ion-exchange to impart a compressive stress to the glass, or that may have been chemically strengthened for another purpose, can be used to prepare an antimicrobial glass according to the second step of the 2-step method described herein.

Glass compositions that can be used in practicing this disclosure include, without limitation, soda lime, alkali aluminosilicate and alkali aluminoborosilicate glasses. Examples of glasses that can be used are disclosed in commonly assigned U.S. Patent Application Publication Nos. 2010/0035038, 2010/0028607, 2010/0009154, 2009/0220761 and 2009/0142568, the teaching of which are incorporated herein by reference. Exemplary alkali aluminosilicate glass compositions, particularly the base glass compositions, suitable for ion-exchange using an ion-exchange bath including silver ions include:

-   -   (a) 60-70 mol % SiO₂; 6-14 mol % Al₂O₃; 0-15 mol % B₂O₃; 0-20         mol % Na₂O; 0-10 mol % K₂O; 0-8 mol % MgO; 0-10 mol % CaO; 0-5         mol % ZrO₂; 0-1 mol % SnO₂; 0-1 mol % CeO₂; less than 50 ppm         As₂O₃; and less than 50 ppm Sb₂O₃; wherein 12 mol %≦Na₂O+K₂O≦20         mol % and 0 mol % MgO+CaO≦10 mol %.     -   (b) 64 mol %≦SiO₂≦68 mol %; 12 mol %≦Na₂O≦16 mol %; 8 mol         %≦Al₂O₃≦12 mol %; 0 mol %≦B₂O₃≦3 mol %; 2 mol %≦K₂O≦5 mol %; 4         mol %≦MgO≦6 mol %; and 0 mol %≦CaO≦5 mol %, and wherein 66 mol         %≦SiO₂+B₂O₃+CaO≦69 mol %; Na₂O+K₂O+B₂O₃+MgO+CaO+SrO≦10 mol %; 5         mol %≦MgO+CaO+SrO≦8 mol %; (Na₂O+B₂O₃)−Al₂O₃≦2 mol %; 2 mol         %≦Na₂O−Al₂O₃≦6 mol %; and 4 mol %≦(Na₂O+K₂O)−Al₂O₃≦10 mol %;     -   (c) 61 mol %≦SiO₂≦75 mol %; 9 mol %≦Na₂O≦21 mol %; 7 mol         %≦Al₂O₃≦15 mol %; 0 mol %≦B₂O₃≦12 mol %; 0 mol %≦K₂O≦4 mol %; 0         mol %≦MgO≦7 mol %; and 0 mol %≦CaO≦mol %;     -   (d) 50 mol %≦SiO₂≦70 mol %; 8 mol %≦Na₂O≦16 mol %; 9 mol         %≦Al₂O₃≦17 mol %; 2 mol %≦B₂O₃≦12 mol %; 0 mol %≦K₂O≦4 mol %; 0         mol %≦MgO≦4 mol %; and 0 mol %≦CaO≦0.2 mol %. wherein the alkali         metal oxides and the alkaline earth metal oxides are modifiers         and the ratio [(mol % Al₂O₃+mol % B₂O₃)÷Σ mol % modifiers] is         greater than 1, that is:         [(mol % Al₂O₃+B₂O₃)=Σ mol % modifiers]>1; and     -   (e) SiO₂>50 mol %; 11 mol %≦Na₂O≦25 mol %; 7 mol %≦Al₂O₃≦26 mol         %; 0 mol %≦B₂O₃≦9 mol %; 0 mol %≦K₂O≦2.5 mol %; 0 mol %≦MgO≦8.5         mol %; and 0 mol %≦CaO≦1.52 mol %.

The alkali aluminosilicate glass and alkali-aluminoborosilicate glasses are substantially free of lithium, meaning any lithium present is as a contaminant, whereas in other embodiments, the alkali aluminosilicate glass is substantially free of at least one of arsenic, antimony, and barium. In other embodiments, the alkali aluminosilicate glass has a liquidus viscosity of at least 130 kilopoise and is down-drawable by those techniques known in the art, for example, but not limited to, fusion-draw processes, slot-draw processes, and re-draw processes. In another embodiment the glass can be made by the float process.

A further example, without limitation, of an alkali aluminosilicate glass that can be used in the present disclosure is one described in the commonly assigned U.S. Patent Application Publication No. 2010/0009154 as having a composition of: 66 mol % SiO₂; 14 mol % Na₂O; 10 mol % Al₂O₃; 0.6 mol % B₂O₃; 2.5 mol % K₂O; 5.7 mol % MgO; and 0.6 mol % CaO; 0.2 mol % SnO₂; and 0.02 mol % ZrO₂. The sodium in this glass, and other exemplary glasses, can be exchanged with, in addition to silver ions, potassium, rubidium, or cesium to produce a region of high compressive stress near the surface and a region under central tension in the interior or central region of a glass part. Unless otherwise specified, it is understood that use of the terms “lithium,” “sodium,” “potassium,” “cesium,” and “rubidium” herein refers to the respective monovalent cations of these alkali metals. If rubidium and cesium are used in the ion-exchange bath they can then also be exchanged for potassium ions as well as for sodium and/or lithium ions in the glass. In one embodiment, some or all of the sodium and/or potassium in the glass composition as-made can be replaced are replaced by lithium in the glass. The lithium can then be ion-exchanged with silver, sodium, potassium, rubidium, or cesium to obtain a high surface compressive stress and an interior volume under tension. In order to produce surface compressive stress (as opposed to tension), one or more of the ions in the glass must be replaced by an ion in the salt solution that has a higher atomic number; for example, silver and sodium replace lithium in the glass, and silver and potassium replace sodium and/or lithium in the glass.

In the examples of the present disclosure, the chemical strengthening of glasses used as an exemplary cover glass article was accomplished in the first step of the disclosed 2-step ion-exchange process where a larger ion such as K⁺¹ (from KNO₃) is exchanged for a smaller ions in the glass, for example Na⁺¹ or Li⁺¹. The base glass, before any ion-exchange, used to prepare the antimicrobial glass sample articles evaluated herein has a composition, in weight percent, falling within the range of 66±2 wt % SiO₂, 13±1.5 wt % Al₂O₃, 13±3 wt % Na₂O 1.5±0.5 wt % K₂O, 4±1 wt % MgO, 0.5±0.2 wt % CaO, less than 1 wt % SnO₂, less than 0.8 wt % ZrO₂ and less than 0.5 wt % Fe₂O₃; and the analyzed specific composition of the base glass actually used to prepare the samples was 66.02 wt % SiO₂, 13.6 wt % Al₂O₃, 13.7 wt % Na₂O, 1.7 wt % K₂O, 3.9 wt % MgO, 0.45 wt % CaO,). 44 wt % SnO₂, 0.04 wt % ZrO₂ and 0.017 wt % Fe₂O₃, This first step can also be accomplished independently by the use of a glass that has already been chemically strengthened by ion-exchange, even though such strengthening was carried out for a different purpose, for example, simply providing a chemically strengthened, but not antimicrobial, glass. Thus, the first step of the 2-step method described herein can be accomplished by either means. In the second step of the 2-step method described herein silver ions are exchanged into the glass using a bath containing both silver and potassium ions, present as for example nitrates, where the AgNO₃ concentration can be in the range 0.1-10 wt % and the ion-exchange is carried out for a time in the range of 1 minute to less then 30 minutes at a temperature in the range of 370° C. to 450° C.

In the examples described herein, KNO₃ was used as the alkali metal in the ion-exchanging salt baths and AgNO₃ was used as the source of silver ion. For all the examples, unless specified otherwise, the ion-exchanges were carried out at 420° C. for the time indicated for sample as described herein.

Method of Quantifying the Surface Ag⁺¹ Concentration

The antibacterial action produced by the silver ions is a “surface effect.” In other words, what is important is the nature and extent of the contact of the microbe with the silver-containing surface of the glass. Therefore a quantitative knowledge of the surface Ag⁺¹ concentration, in μg/cm² or ions/cm², is crucial in ascertaining the effectiveness of the antimicrobial action. This is even more pertinent in the present case where the Ag is being added by an ion-exchange process. The analytical techniques of EMP (electron microprobe) and XPS (X-ray photoluminescence spectroscopy) and SIMS (secondary ion mass spectroscopy) can be used to obtain the Ag⁺¹ profile, but they yield volume concentration values, albeit close to the surface, whereas what is important is the surface ion concentration. EMP and XPS can quantitatively determine the Ag⁺¹ concentration to within 10-20 nm. TOF-SIMS (time-of-flight secondary ion mass spectroscopy) can look nearer to the surface but it is non-quantitative. What makes the estimate of the surface concentration more difficult is that the Ag⁺¹ concentration actually decreases as one nears the surface as shown from the EMP measurements of FIG. 4. FIG. 4 is graph of EMP results showing the actual silver ion concentration, calculated Ag₂O, versus depth for glass samples that were prepared by the 2-step method using different concentrations of AgNO₃ in the second bath, where the first IOX bath was 100 wt % KNO₃ and the second IOX baths were KNO₃ baths containing 1 wt % (♦), 2 wt % (▪) or 5 wt % (▴) AgNO₃, respectively, and the second bath ion-exchange time and temperature were 20 minutes and 420° C., respectively.

The following Table 3 gives the Ag ion bath concentrations, the time for ion-exchange and the resulting EMP measurements, as wt % Ag₂O, for several different ion-exchanges. Except for the sample ion-exchanged for 300 minutes, the samples in Table 3 were prepared using the 2-step method. The sample having an ion-exchange time of 300 minutes was prepared by the 1-step method using the same ion-exchange bath having the same composition as the second bath of the 2-step process. All the glass articles of Table 3 have a compressive stress of at least 250 MPa. In one embodiment the compressive stress is at least 500 MPa. In another embodiment the compressive stress is at least 600 MPa. The number term “EMP (15 nm)” refers to a depth which is close as close as the accelerating potential of the method allows. All ion-exchanges of Table 3 were carried out at 420° for both the 1-step sample and the 2-step samples. In the 2-step process the first ion-exchange was done using KNO₃ only for a time of 5.5 hours, and the second ion-exchange was done using an AgNO₃/KNO₃ bath. The Ag/K bath compositions are given in Table 3.

TABLE 3 Ag wt % in bath IOX time, minutes EMP (≅15 nm), wt % 0.15* 20  0.82 0.15‡ 330 1.0 (5.5 hours) 0.25* 20 1.0 0.5* 20 2.2 1.0* 20 5-7 2.0* 20 7.1-8.1 5.0* 20 12.3-15.3 10.0* 10 23-25 Wt % was calculated as the oxide, Ag₂O *= made using the 2-step process ‡= made using the 1-step process

The EMP method used was to vary the accelerating potential to access different depths in the glass samples. The glasses of FIG. 5 are the measured values of the wt % Ag₂O vs. depth as a function of the AgNO₃ bath concentration in the 2^(nd) step of the 2-step process described above.

XPS (x-ray photoluminescence spectroscopy), was also used to estimate the Ag concentration. Although XPS is usually referred to as a surface measurement, it actually measures to a depth 5-10 nm, with approximately 95% of the signal coming from ≦5 nm of the surface. Therefore XPS data should also be interpreted in a way similar to that used to interpret the EMP while data recognizing that the XPS data is from an area closer to the surface of the glass. The XPS results are reported as an atomic percent of the atoms on the surface of the glass substrate and are shown in Table 4. Table 4 also includes the EMP results for the same samples that were XPS analyzed. In Table 4 the samples showing an ion-exchange time of 5.5 hours were prepared using the 1-step method. The sample having an ion-exchange time of 20 minutes was prepared using the 2-step method AG IOX was carried out in the second step.

TABLE 4 Comparison of Ag concentration from XPS and EMP estimates IOX Ag⁺¹ Ag₂O Wt % Ag₂O Ag Wt % Time at At % XPS Wt % in Bath 420° C. XPS (calc) EMP N/cm³ 0.1‡ 5.5 hours 0.98 2 2   2 × 10²⁰ 5%* 20 minutes 9.2 19 19 2.28 × 10²¹ 5%‡ 5.5 hours 12.6 26 24 3.00 × 10²¹ *= 2-step method ‡= 1-step method

The agreement in the amount of Ag₂O is excellent, thus indicating that both methods are measuring the same volume concentration.

While the data presented above provides estimates of the volume concentration, the following paragraphs describe how to determine the actual surface concentration since this is the relevant number pertaining to antimicrobial behavior. Silver in the body of the glass below the surface plays no antimicrobial role since it has no access to the bacteria on the surface.

Determination of the surface concentration can also be done using a statistical method. The relationship is simply derived from the idea of an array of particles N along a line defined as N/cm. Extending this array this to a plane gives one surface concentration N²/cm², and similarly extending it to a cube provides a volume concentration N³/cm³. The fact that the array is disordered is not a limitation as long as one can define an average. In other words, an isotropic homogeneous array of particles allows an average number of particles per unit dimension to be defined. This approach allows one to define the relationship between the surface concentration and the volume concentration as shown in the following Equation 1. N/cm² =[N/cm³]^(2/3)  Eq. 1. Using the EMP volume concentration estimates for various IOX schedules, one can make the graphs shown in FIGS. 6A and 6B. FIG. 6A, is a graph of the Ag-ion surface concentration in ions/cm²×10¹⁴ versus the Ag₂O concentration in wt %. One can also calculate the values of the surface concentration in μg/cm². The conversion of the estimates of surface concentration given above to units of μg/cm² allows comparison to some of the literature.

For the estimate from equation 1, one must use the N/cm² to convert to μg/cm² as shown in Equation 2.

$\begin{matrix} {\frac{\mu\; g}{{cm}^{2}} = {{\frac{N}{{cm}^{2}}\frac{1}{A}{MWAg}} = {\left( {N/{cm}^{2}} \right)\left( {1.8 \times 10^{- 22}} \right)}}} & {{Eq}.\mspace{14mu} 2} \end{matrix}$ FIG. 6B, is the surface concentration expressed in μg/cm² vs. wt % Ag₂O in the glass

The 2-step method permits much higher Ag⁺¹ surface concentration to be achieved without any other undesirable effects. The very important and unique advantage of the higher surface concentration is the decrease in the bacteria “kill” time. This is the time that is required to produce a significant log reduction ≧2 as described below. FIG. 8 shows the dependence of the “kill” time as a function of the surface concentration using samples prepared by the 2-step method to have varying surface concentrations which were determined as described herein. The value of the “kill” time is a significant feature of the intended applications for all uses including hand-held device applications. It is only by using the 2-step method can one produce “kill” times of any practical utility as will be shown below, particularly for electronic devices colored cover or touch screen would impair the user's visual experience.

It was further noted that the silver ion concentration increases as one goes further into the glass from the surface. While the origin of this phenomenon is uncertain, it was verified as real by a comparison of bacterial Log Reduction values as shown in FIG. 7 for a silver ion exchanged glass. FIG. 7 is a graph comparing the antimicrobial activity, as log reduction versus time, for a silver ion containing glass as prepared by the 2-step method using a second IOX bath containing 0.15 wt % Ag. Sample A (diamond ♦) represents the antimicrobial glass as prepared using the (0.15 wt % Ag bath, and Sample A-R (square ▪) represents the same glass after the removal of 1 μm of the glass surface. The data of FIG. 7 indicate that the while Samples A and A-R have achieve substantially the same Log Reduction value during the during first approximately 100 minutes, after approximately 250 minutes the A-R Sample, which had the top 1 μm of glass removed, exhibited a much higher Log Reduction value. This illustrates that the Ag content actually increases as the distance from the surface increases and the importance of having as high a surface concentration as possible to maximize antimicrobial activity.

Antimicrobial Testing

Antibacterial tests were carried out using cultured gram negative E. coli; DH5alpha-Invitrogen Catalog No. I8258012, Lot No. 7672225, rendered Kanamycin resistant through a transformation with PucI9 (Invitogen) plasmid). The bacteria culture was started using either LB Kan Broth (Teknova #L8145) or Typtic Soy Broth (Teknova #T1550). Approximately 2 μl of liquid bacteria suspension or a pipette tip full of bacteria were streaked from an agar plate and dispensed into a capped tube containing 2-3 ml of broth and incubated overnight at 37° C. in a shaking incubator. The next day the bacteria culture was removed from the incubator and washed twice with PBS. The optical density (OD) was measured and the cell culture was diluted to a final bacterial concentration of approximately 1×10⁶ CFU/ml. The cells were placed on the selected glass surface, antimicrobial or not antimicrobial (the control) for 6 hours at a temperature of 37° C. The buffers from each well were collected and the plates were twice washed with ice-cold PBS. For each well the buffer and wash were combined and the surface spread-plate method was used for colony counting.

Antimicrobial properties were exhibited in glass samples prepared using 1-step and 2-step methods. The control sample in all cases is an ion-exchanged glass that does not contain silver. Each of the glass samples was cut into a glass slide of 1×1 square inch (2.54 cm×2.54 cm square) and placed in a Petri dish. Three glass slides were used as negative controls. Gram negative E. coli bacteria were suspended in a 1/500 LB medium at a concentration of 1×10⁶ cells/ml. 156 μl of E. coli cell suspension was placed onto each sample surface and held in close contact by using a sterilized laboratory PARAFILM®, and incubated for 6 hours at 37° C. at saturation humidity (>95% relative humidity). Each sample was produced in triplicate. After 6 hours incubation, 2 ml of PBS buffer was added into each Petri dish. After shaking, both the slide and PARAFILM® were washed, and all the solution from each Petri dish was collected and placed onto a LB agar plate. After further 16-24 hour incubation at 37° C., the bacteria colony formation on the agar plate was examined. The results are shown by the bacterial growth response: Log reduction=−Log(C_(a)/C₀), where C_(a) is the concentration of bacteria (or virus or fungus) after exposure to the antimicrobial surface and C₀ is the concentration of bacteria of the control sample in which the bacteria is not in contact with an antimicrobial surface. As an example, a Log Reduction of 3=99.9% of bacterial or virus killed and a Log Reduction of 5=99.999% of bacteria or virus killed. The following Table 5 shows log reduction vs. surface Ag concentration.

For the purposes of the test and to insure that no bacterial contamination was initially present on the glass before the testing began, all the ion-exchanged glass samples, with or without silver, were sterilized by washing with 70 Vol. % ethanol for 1 minutes and wiped using distilled water. Table 5 show the results of bacterial testing results of glass samples after 6 hours using antimicrobial glass having surface silver ion concentrations, calculated as Ag₂O, as described in Table 5. The glasses in Table 5 were all prepared by the 2-step method. The first step IOX was carried out using a 100 wt % KNO₃ bath for a time in the range of 5-6 hours at a temperature of approximate 420°. The second step IOX was carried out using The surface Ag⁺¹ concentration, calculated in μg/cm², was determined as described herein

TABLE 5 Bacterial test: 2-Step Antimicrobial Glass Showing LR >5 After 6 Hours Sample, Ag⁺¹, μg/cm² 2^(nd) Step IOX Conditions Log Reduction 0.0155 420° C., 5 minutes  >5 0.0155 420° C., 10 minutes >5 0.016 420° C., 20 minutes >5 0.03 420° C., 5 minutes  >5 0.0325 420° C., 10 minutes >5 0.036 420° C., 20 minutes >5

Table 6 Illustrates that the rate of bacterial reduction is faster for samples prepared using the 2-step method when compared to the 1-step method.

TABLE 6 Bacterial Test Results Time, minutes 1-Step Method 2-Step Method 0 0 0 45 0.23 0.34 90 2.95 3.7 180 >5 >5 270 >5 >5 360 >5 >5 Antiviral Test

An antiviral test was carried out using an Ag ion-exchanged glass having a surface ion concentration of 0.03 μg/cm² and HIV as the test virus. A Log Reduction of 2.22 was obtained after 1 hour.

Cytotoxicity Test

Cytotoxicity studies were conducted using NIH3T3 mouse fibroblast cells for culturing. Glass slides, 1×1 square inch (25.4 mm×25.4 mm), were attached to the bottom of a 96-well Holey plate. For the purposes of the test and to insure that no bacterial contamination was initially present on the glass before the cytotoxicity testing began, all the ion-exchanged glass samples, with or without silver, were sterilized by irradiation with UV light for 10-30 minutes, soaked in 70 Vol. % for 15 minutes and then wiped using distilled water. Four wells were cultured for each glass slide. The seeding density of each well was approximately 2×10⁴ cells per well. After seeded wells were incubated for three days at 37° C. they were visually inspected using a live/dead stain and a fluorescence microscope for the counting of dead cells or colonies. No dead cells were observed for Samples C1, C2, C3 and C4 (Table 7).

TABLE 7 Sample Ag μg/cm² Cytotoxicity C0 0 0 = No cytotoxicity observed C1 0.015 0 C2 0.005 0 C3 0.065 0 C4 0.08 0 C0 = Control, IOXed aluminosilicate glass, No Ag C1-C4 = prepared by the 2-step process as indicated; in μg/cm²

For use in hospitals and laboratories where mammalian cells infected with bacteria, viruses or fungi may be present, and coloring of the glass is not a consideration, higher concentrations of silver ions can be attained using the methods described herein.

Coatings

Another important aspect of the disclosure are the methods by which the antimicrobial behavior is maintained when selected functional coatings (including films) are placed on the surface of the antimicrobial, chemically strengthened glass. For example, in many touch screen applications (phones, computers, ATMs, etc) where the glass is used as a cover glass, a coating or film is placed on the glass surface so that fingerprints can be cleaned relatively easily. The coating(s) that facilitate cleaning are low surface energy coatings, for example, coatings in the class of “fluoroalkylsilanes” of general formula A_(x)-Si—B_(4-x), where A is selected from the group consisting of perfluoroalkyl R_(F)—, perfluoroalkyl terminated perfluoropolyether, perfluoroalkyl-alkyl, copolymers of fluoroalkene silanes and alkene silanes, and mixtures of fluoroalkylsilanes and hydrophilic silanes, B is Cl, acetoxy [CH₃—C(O)—O—] or alkoxy [for example CH₃O— or C₂H₅O—], and x=1 or 2. Low surface energy coatings of the foregoing types are commercially available from different manufacturers, for example, Dow Corning, [DC2634—a perfluoropolyether silane in which the functional perfluoro moiety is Poly[oxy(1,1,2,2,3,3-hexafluoro-1,3-propanediyl)], α-(heptafluoropropyl)-ω-[1,1,2,2-tetrafluoro-3-(2-propenyloxy)propoxy]; Gelest [SIT8174.0, Tridecafluorotetrahydrooctyltrichlorosilane; SIT8371.0, Trifluoropropyltrichlorosilane; SIH5841.0 Heptadecafluorotetrahydrodecyl trichlorosilane; and SIH5841.0 (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trichlorosilane; SIH5841.5 (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trimethoxysilane; and SIH5841.2 (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane]; Cytonix [FSM 1200 Perfluoropolyether mono-silane; FSD 2500 Medium molecular weight perfluoropolyether di-silane; FSD 4500 High molecular weight perfluoropolyether polysilanes]. The low surface energy coating should have a spacer or skeletal chain length in the range of 1 nm-20 nm, the skeletal chain being carbon atoms or a mixture of carbon and oxygen atoms in the case of the perfluoropolyethers. In one embodiment the chain length is in the range of 2 nm to 20 nm. In a further embodiment the chain length is in the range of 1-10 nm. Other examples are

(a) copolymers of fluoroalkene silanes and alkene silanes; and

(b) mixtures of fluoroalkylsilanes and hydrophilic silanes.

Silanes other than the foregoing can also be used provided that they do not prevent water vapor from reaching the surface of the glass so that silver ions can be transported from the glass surface to the microbe to thereby kill the microbe or inhibit its growth.

Generally, the fluoro-containing coatings describe above have 1 or 2 fluorocarbon-containing moieties attached to the silicon and each of the moieties, independently, have a chain length in the range of 1 nm to 20 nm, and the chain may include oxygen atoms or sulphur atoms along the chain. In one embodiment the chain length is in the range of 2 nm to 20 nm. In a further embodiment the chain length is in the range of 1-10 nm. What is important for the coating is that at least part the fluorocarbon moiety be sufficiently distant from the surface so that water molecules can come into contact with the surface, pick up silver ions on the surface, and transport the silver ions to a microbe where they can be absorbed in to microbe and thus kill it or decrease its reproductive rate. Consequently, it is preferred that one or two fluorocarbon moieties be attached to the silicon atom and that the silicon atom be bonded to the glass by two or three Si—O bonds. For example, if the alkyl group of (a) above, which functions as a spacer or skeletal chain between the silver-containing glass surface and the fluorocarbon moiety, is too short, then hydrophobic fluorocarbon moiety can block water molecules from reaching the glass surface and thus silver ions cannot be transported from the surface to and into the microbe. In another instance, without being held to any particular theory, it is believed that the oxygen atoms in a perfluoropolyether alkoxy silane that has been bonded to the surface of the antimicrobial glass can facilitate the migration of water molecules by oxygen atoms along the chain to the surface where the water molecules can coordinate to silver ions and facilitate the ions transport to the microbe. An exemplary perfluoropolyether alkoxy silane is Dow Corning® 2634 used as 0.02-1 wt % solutions in a fluorinated solvent. After the coating material was applied to the antimicrobial glass article such as described herein, the coating was cured to adhere the coating to the surface of the glass article and finally sonicated in a fluorinated solvent (for example, Novec™ HFE7200, 3M Company) bath for a 3 minutes remove any unreacted coating material. The curing was done thermally by either heating the coated in an oven, for example, at 50° C., 50% RH, for a cure time as suggested by the manufacturer or by infrared heating of the coated articles. The coated article was then heated in an oven for a time in the range of 30 minutes to 2 hours to cure the coating material to the glass surface.

The method and process for the deposition of these coatings is capable of controlling the thickness and morphology of the coating on the surface of the glass. Process methods and steps can be introduced where the coating was deposited in such a fashion either to be discontinuous or quasi-discontinuous. Such process methods include, but are not limited to, vapor deposition or spray coating through a predetermined coverage mask, ink jet printing, micro contact printing using a master which would allow the fluorosilane to be coated in specific regions, humidity curing to allow phase separation of the fluorosilane. When the coating is sufficiently thin it can be continuous. Thin continuous coatings can be deposited, for example, by dip, spray and vapor deposition followed by curing to adhere the silanes, and followed by ultrasound cleaning to remove un-reacted but physically adsorbed silanes. The foregoing procedures allow the antimicrobial action to persist in open uncoated areas, or in areas where the coating is very thin or the surface is coating-free while at the same time maintaining intended functional performance of the coating. FIG. 2 is an AFM (atomic force micrograph) illustrating this desired morphology in the form of localized domains (islands-in-the-sea) of fluorosilane deposited on the surface of a silver ion containing, chemically strengthened glass as described herein. In FIG. 2 the glass (or sea) is the black background and the coating domains or islands 100 are shown as the white to gray dots or ovals of various sizes that are dispersed on the background. In the case where the coating is continuous, the coating is relatively thin, having a thickness, in one embodiment, in the range of 0.5 nm to 20 nm in order for the antimicrobial activity of the glass surface to remain effective. In another embodiment the thickness of the coating is in the range of 0.5 nm to 5 nm. In a further embodiment the thickness of the coating is in the range of 1 nm to 3 nm. In the thin coating case a mixed self-assembled monolayer can be prepared on the surface using two silanes, where one silane is a fluoroalkylsilane and the other silane is a hydrophilic silane (for example, a polyethylene glycol containing silane), wherein the hydrophilic or “water loving” silane domains assist in the antimicrobial action by capturing water molecules and presenting them to the surface where the water can pick up silver ions for transport to the microbe. In one embodiment fluoro-oligoethylene glycol silanes can also be used, where the oligoethylene glycol part of the silanes can assist in capturing free water at the interface.

The test method used for determining antibacterial properties of a silver-containing glass having a hydrophobic coating thereon was a modified version of the JISZ-2801: 2000 method, which is a Japanese Industrial Standard that was developed to measure the antibacterial activity of hydrophobic materials, particularly polymers into which silver ions had been incorporated. The antibacterial activity is measured by quantitatively by determining the survival of bacteria cells that have been held in intimate contact with a surface thought to be antibacterial and incubated for 24 hours at 35° C. After the time period has elapsed the cells are counted and compared to a non-treated surface. The test was modified in that for the incubation period was changed to 6 hours at 37° C. After 6 hours the samples were removed from the incubator and the entire testing surface was thoroughly washed with PBS to ensure that all bacteria were removed. The cells and the PBS wash were then transferred to a broth agar plate for overnight culture. After a period of 16-24 hours the bacterial colonies on the agar plate were counted. FIG. 3 is a diagram illustrating the modified method that was used. In FIG. 3 numeral 10 represents the addition of a 400 μl bacterial suspension of concentration 1×10⁶ cells/ml to the sample plates 12 which can be either a Ag-containing glass plate or a control (no Ag) plate, covering 14 the plates having a bacterial suspension thereon with the PARAFILM® resulting in PARAFILM® covered plates 16, and thereafter incubating the bacteria at 37° C. for 6 hours as indicated by 18, and lastly counting the colonies as represented by 20. The samples were tested using E. coli (gram negative) bacteria.

Table 8 presents E. coli antibacterial results obtained using 2-step Ag ion exchanged glass with varying surface concentrations followed by a deposition of the coating. The Control Sample was ion-exchanged using a 100% KNO₃ bath (no AgNO₃). The coating material was a fluorosilane which was applied to a thickness in the range of 0.5 nm to 5 nm and was uniform across the surface of the glass. After coating the samples were cured to adhere the silane to the surface of the glass article and finally sonicated in a fluorinated solvent bath to remove unreacted silanes.

TABLE 8 Sample IOX Bath % reduction Time, hours S10-NC Control, 100% KNO₃ 0 NA S10-C Control, 100% KNO₃ 0 NA S12-NC 0.015 ug/cm2 99.9 ≧3 S13-C 0.015 ug/cm2 99.9 ≧3 S14-NC 0.033 ug/cm2 99.9 ≦2 S14-C 0.033 ug/cm2 99.9 ≦2 S10 is the control sample. NC = no coating C = coated Bacterial suspension was E. coli prepared as previously described. Coating was a hydrophobic coating material of less than 20 nm thickness. The tests were repeated twice from the start and produced the same results.

There is minimal impact on the compressive stress using the 2-step method, because the depth of the Ag ion exchange into the glass in the second step is so shallow, the compressive stress of the glass, which was chemically strengthened in a first step by ion-exchange of larger ions, typically potassium or larger alkali metal ions, for smaller ions in the glass as prepared, typically sodium and lithium ions, the compressive stress of the glass is not measurably affected. Further, it is noted that the ionic radius of silver and potassium ions are substantially the same, the Pauling ionic radii of silver and potassium being 1.26 and 1.33 Angstroms, respectively. Consequently, an ion-exchange of silver ions for potassium ions already in the glass after the first step ion-exchange will have a minimal effect on the compressive stress of the glass. Table 9 compares the compressive stress of the glass samples after the first the first ion-exchange step, KNO₃ exchange only, and after the second ion-exchange step using a bath containing both AgNO₃ and KNO₃. The samples were tested using the Ring-on-Ring test both before and after abrasion. The values in Table are the average of 3-4 sample tests and the standard deviation is given. Samples were prepared using the 2-step ion-exchange method described herein. The first step ion-exchange was carried out for 5.5 hours using a 100% KNO₃ bath at 420° C. A plurality of samples was set aside after the first ion-exchange step was completed. The remainder of the samples were then subjected to the second ion-exchange step for 20 minutes using a 5 wt % AgNO₃/95 wt % KNO₃ at 420°

TABLE 9 Before After Step 1 Step 2 Abrasion SD Abrasion SD Sample KNO₃ AgNO₃/KNO₃ MPa MPa MPa MPa 1 Yes No 970 ±90 2 Yes Yes 800 ±260 — — 1A Yes No — — 380 ±40 2A Yes Yes — — 400 ±40 Samples 1 and 2 results are samples as-made and before abrasion. Samples 1A and 2A results are for samples after abrasion. SD = Standard Deviation The results shown in Table 9 indicate that the second ion-exchange step with the AgNO₃/KNO₃ has a minimal effect on the compressive stress.

In an additional embodiment the disclosure is to a method of making an antimicrobial, chemically strengthened glass article, said method comprising providing glass article having a first surface, a second surface and a selected thickness between said surfaces, and alkali metal ions in the glass; providing a first ion-exchange bath consisting of at least one alkali metal ion larger that the alkali metal ions in the provided glass to impart a compressive stress greater than 500 MPa into the glass; providing a second ion-exchange bath consisting essentially of 0.005 wt % to 5.0 wt % silver nitrate, the remainder of the bath consisting of the at least one of the alkali metal ions in the first bath; ion-exchanging with the second bath to thereby incorporate said silver and said alkali metal ion(s) into at least one of said surfaces to form a glass article having a compressive stress of greater than 250 MPa and at least one an antimicrobial, chemically strengthened surface; and the concentration of silver ion on the surface of the glass is in the range of greater than zero to less than 0.047 μg/cm².

Thus, in one embodiment the disclosure is to an antimicrobial, chemically strengthened glass comprising a glass article having a compressive stress layer extending from the surface of the glass to a selected depth in the glass; an antimicrobial Ag+ region that is part of the compressive stress layer of the glass article; wherein the compressive stress in the glass is at least 250 MPa and the surface concentration of the Ag⁺¹ ion is in the range of greater than zero to less than or equal to 0.047 μg/cm². The glass further comprises a low surface energy coating on the surface of the glass having the characteristic of allowing water molecules to reach the Ag+ ions in the glass. The glass is capable of inhibiting at least 2 microbes species to a Log Reduction greater that 1 within 1 hour. In an embodiment the glass has an antibacterial Log Reduction of greater than 4 after 6 hours. In another embodiment the glass has an antibacterial Log Reduction of greater than 5 after 6 hours. In a further embodiment the glass has an Ag⁺¹ ion surface concentration in the range of 0.005 μg/cm² to 0.035 μg/cm² and is non-cytotoxic. In an additional embodiment the glass has an Ag⁺¹ ion surface concentration in the range of 0.01 μg/cm² μg/cm² to 0.035 μg/cm² and is non-cytotoxic. In an embodiment the glass has an Ag⁺¹ ion surface concentration in the range of 0.015 μg/cm² μg/cm² to 0.030 μg/cm² and is non-cytotoxic. In another embodiment the compressive stress is at least 500 MPa. In an additional embodiment the compressive stress is at least 600 MPa. The low surface energy functional coating has a terminal perfluorinated moiety and is selected from the group consisting of silanes of general formula A_(x)-Si—B_(4-x), where A is perfluoroalkyl R_(F)—, perfluoroalkyl terminated perfluoropolyether, perfluoroalkyl-alkyl, copolymers of fluoroalkene silanes and alkene silanes, and mixtures of fluoroalkylsilanes and hydrophilic silanes, B is Cl, acetoxy [CH₃—C(O)—O—] or alkoxy, and x=1 or 2; and the coating has thickness in the range of 0.5 nm to 20 nm and is bonded to the surface of the glass by at least one SiO bond between the coating silicon atom and an glass oxygen atom. The coating has a skeletal chain length from the silicon atom to its end, for example, a final CF₃ moiety, that is in the range of 2 nm to 20 nm, the skeletal chain consisting of at least one selected from the group consisting of (a) carbon atoms and (b) a combination of carbon and oxygen atoms in the case of polyethers. In an embodiment the coating is a perfluoroalkyl alkoxy silane of formula (R_(F1))_(x)—Si(OR)_(4-x), where x=1 or 2, R_(F1) moiety is a perfluoroalkyl group having a carbon chain length in the range of 2 nm to 20 nm and OR is acetoxy, —OCH₃ or OCH₂H₃. In another embodiment the coating is (RO)_(4-z)—Si—[(CH₂)₃—OCF₂—CF₂—[OCF₂—CF₂—CF₂]_(n)—F]_(z), where z=1 or 2, n is an integer sufficient to provide that [(CH₂)₃—OCF₂—CF₂—[OCF₂—CF₂—CF₂]_(n)—F] has a chain length in the range of 2 nm to 20 nm, and RO═CH₃O—, CH₃—CH₂O—, or CH₃C(O)O—. In a further embodiment the coating is a perfluoroalkyl alkyl alkoxy silane of formula RO)_(4 z)—Si—[(CH₂)_(x)—(CF₂)_(y)—CF₃]_(z), where x+y are integers whose sum is sufficient to provide that [(CH₂)_(x)—(CF₂)_(y)—CF₃] has a length in the range of 2 nm to 20 nm, with the provision that y≧x, z is 1 or 2, and RO═CH₃O—, CH₃—CH₂O—, or CH₃C(O)O—.

In an embodiment the antimicrobial, chemically strengthened glass is selected from the group consisting of an antimicrobial, chemically strengthened alkali aluminosilicate glass and an alkali aluminoborosilicate glass, and the glass has a silver ion surface concentration in the range of 0.01 μg/cm² and 0.035 μg/cm², and the glass surface is not cytotoxic. In an embodiment the transmission of the glass, uncorrected for reflection losses, over the wavelength range of 400 nm to 750 nm is at least 88%. In another embodiment the ratio of the transmission at 428 nm/650 nm is at least 99%.

In addition the disclosure is thus further directed to a method of making an antimicrobial, chemically strengthened glass article comprising providing glass article having a first surface, a second surface and a selected thickness between said surfaces, and alkali metal ions in the glass; providing a first ion-exchange bath consisting of at least one alkali metal ion larger that the alkali metal ions in the provided glass to impart a compressive stress greater than 250 MPa into the glass; providing a second ion-exchange bath consisting essentially of 0.005 wt % to 5.0 wt % silver nitrate, the remainder of the bath consisting of the at least one of the alkali metal ions in the first bath; ion-exchanging with the second bath to thereby incorporate said silver and said alkali metal ion(s) into at least one of said surfaces to form a glass article having a compressive stress of greater than 250 MPa and at least one an antimicrobial, chemically strengthened surface; and wherein the concentration of silver ion on the surface of the glass is in the range of greater than zero to less than 0.047 μg/cm² and the second bath ion-exchange time is less than 30 minutes. In one embodiment the compressive stress is greater than 500 MPa. The second ion-exchange bath consists of silver nitrate in an amount in the range of 0.15 wt % to 10 wt %, and the remainder of the bath is potassium nitrate. In one embodiment the second bath ion exchange time is less than or equal to 20 minutes. In another embodiment the second bath ion exchange time is less than or equal to 10 minutes. The provided glass article is selected from the group consisting of soda lime glass, alkali aluminosilicate glass and alkali aluminoborosilicate glass articles. In one embodiment the provided glass is selected from glasses having a composition:

-   -   (a) 60-70 mol % SiO₂; 6-14 mol % Al₂O₃; 0-15 mol % B₂O₃; 0-15         mol % Li₂O; 0-20 mol % Na₂O; 0-10 mol % K₂O; 0-8 mol % MgO; 0-10         mol % CaO; 0-5 mol % ZrO₂; 0-1 mol % SnO₂; 0-1 mol % CeO₂; less         than 50 ppm As₂O₃; and less than 50 ppm Sb₂O₃; wherein 12 mol         %≦Li₂O+Na₂O+K₂O≦20 mol % and 0 mol %≦MgO+CaO≦10 mol %;     -   (b) 64 mol %≦SiO₂≦68 mol %; 12 mol %≦Na₂O≦16 mol %; 8 mol         %≦Al₂O₃≦12 mol %; 0 mol %≦B₂O₃≦3 mol %; 2 mol %≦K₂O≦5 mol %; 4         mol %≦MgO≦6 mol %; and 0 mol %≦CaO≦5 mol %, and wherein 66 mol         %≦SiO₂+B₂O₃+CaO≦69 mol %; Na₂O+K₂O+B₂O₃+MgO+CaO+SrO≧10 mol %; 5         mol %≦MgO+CaO+SrO≦8 mol %; (Na₂O+B₂O₃)−Al₂O₃≦2 mol %; 2 mol         %≦Na₂O−Al₂O₃≦6 mol %; and 4 mol %≦(Na₂O+K₂O)−Al₂O₃≦10 mol %;     -   (c) 61 mol %≦SiO₂≦75 mol %; 9 mol %≦Na₂O≦21 mol %; 7 mol         %≦Al₂O₃≦15 mol %; 0 mol %≦B₂O₃≦12 mol %; 0 mol %≦K₂O≦4 mol %; 0         mol %≦MgO 7≦mol %; and 0 mol %≦CaO≦mol %;     -   (d) 50 mol %≦SiO₂≦70 mol %; 8 mol % Na₂O≦16 mol %; 9 mol         %≦Al₂O₃≦17 mol %; 2 mol %≦B₂O₃≦12 mol %; 0 mol %≦K₂O≦4 mol %; 0         mol %≦MgO≦4 mol %; and 0 mol %≦CaO≦0.2 mol %. wherein the alkali         metal oxides and the alkaline earth metal oxides are modifiers         and the ratio [(mol % Al₂O₃+mol % B₂O₃)÷Σ mol % modifiers] is         greater than 1, that is:         [(mol % Al₂O₃+B₂O₃)÷Σ mol % modifiers]>1; and     -   (e) SiO₂>50 mol %; 11 mol %≦Na₂O≦25 mol %; 7 mol %≦Al₂O₃≦26 mol         %; o mol %≦B₂O₃≦9 mol %; 0 mol %≦K₂O≦2.5 mol %; 0 mol %≦O≦8.5         mol %; and 0 mol %≦CaO≦1.52 mol %; wherein the foregoing are         substantially lithium free.

The method further comprises the step of applying a low surface energy coating to said at least one antimicrobial, chemically strengthened glass surface, the coating being selected from the group consisting of fluoroalkylsilanes, perfluoropolyether alkoxy silanes, perfluoroalkyl alkoxy silanes, fluoroalkylsilane-(non-fluoroalkylsilane) copolymers, and mixtures of fluoroalkylsilanes and hydrophilic silanes; and curing the applied coating to thereby bond the coating to the glass by a Si—O bond between the coating and the glass; wherein the functional coating has a thickness in the range of 0.5 nm to 20 nm. In one embodiment the low surface energy functional coating is a perfluoroalkyl alkoxy silane of formula (R_(F1))_(x)—Si(OR)_(4-x) , where x=1 or 2, R_(F1) moiety is a perfluoroalkyl group having a carbon chain length in the range of 16-130 carbon atom and OR is acetoxy, —OCH₃ or OCH₂H₃. In another embodiment the low surface energy functional coating bonded to the antimicrobial, chemically strengthened glass is a perfluoropolyether alkoxy silanc of formula [CF₃—(CF₂CF₂O)_(a)]_(x)—Si(OR)_(4-x) where a is in the range of 5-10, x =1 or 1, and OR is acetoxy, —OCH₃ or OCH₂H₃, wherein the total perfluoroether chain length from the silicon atom to the end of the chain at its greatest length its end is in the range of 1 nm to 10 nm, 16 to 130 atoms. In a further embodiment the low surface energy functional coating bonded to the antimicrobial, chemically strengthened glass is a perfluoroalkyl alkyl alkoxy silane of formula [R_(F2)—(CH₂)_(b)]_(x)—Si(OR)_(4-x) where R_(F2) is a perfluoroalkyl group having a carbon chain length in the range of 10-16 carbon atoms, b is in the range of 14-20, x=2 or 3 and OR is acetoxy, —OCH₃ or OCH₂CH₃. In one embodiment the low surface energy functional coating is applied to form domains on the surface of the glass and a non-domain area without coating. In another embodiment the low surface energy applied uniformly/continuously across the glass surface and has a thickness in the range of 0.5 nm to 10 nm. In one embodiment the thickness in the range of 1 nm to 3 nm. The method produces as glass having a transmission of the glass, uncorrected for reflection losses, over the wavelength of 400 nm to750 nm is at least 88%., and also the ratio of the transmission at 428 nm/650 nm is 99%.

For use as antimicrobial shelving, table tops and other applications in hospitals, laboratories and other institutions handling biological substances, where color in the glass is not a consideration, glass having a silver ion surface concentration of greater than 0.035 μg/cm² may be suitable. Glass having a silver ion surface concentration of 0.5 or higher may be prepared using the methods described herein.

While typical embodiments have been set forth for the purpose of illustration, the foregoing description should not be deemed to be a limitation on the scope of the disclosure or the appended claims. Accordingly, various modifications, adaptations, and alternatives may occur to one skilled in the art without departing from the spirit and scope of this disclosure or the appended claims. 

We claim
 1. A method of making an antimicrobial, chemically strengthened glass article, said method comprising: providing a glass article having a first surface, and a plurality of ion exchangeable alkali metal ions; providing a first ion-exchange bath comprising a plurality of first ion exchanging alkali metal ions, each having a larger size than the size of the ion exchangeable alkali metal ions, and ion exchanging a portion of the plurality of ion exchangeable alkali metal ions in the glass article for the first ion exchanging alkali metal ions in the first ion-exchange bath to impart a compressive stress greater than 250 MPa into the glass article; providing a second ion-exchange bath comprising 0.005 wt % to 10 wt % silver nitrate having a plurality of silver ions and a plurality of the first ion exchanging alkali metal ions; ion-exchanging the glass article with the compressive stress greater than 250 MPa in the second ion-exchange bath to ion exchange a portion of the silver ions and a portion of said first ion exchanging alkali metal ions into the first surface to form a glass article having a compressive stress of greater than 250 MPa and at least one antimicrobial surface; and wherein the concentration of silver ions at the first surface of the glass article having a compressive stress greater than 250 MPa and at least one antimicrobial surface is in the range of greater than zero to less than 0.080 μg/cm².
 2. The method according to claim 1, wherein the compressive stress is greater than 500 MPa.
 3. The method according to claim 1, wherein the second ion-exchange bath comprises silver nitrate in an amount in the range of 0.15 wt % to 5 wt %, and wherein the first ion exchanging metal ions comprise potassium metal ions.
 4. The method according to claim 1, wherein ion-exchanging the glass article with the compressive stress greater than 250 MPa in the second ion-exchange bath is conducted for less than or equal to 30 minutes.
 5. The method according to claim 1, wherein ion-exchanging the glass article with the compressive stress greater than 250 MPa in the second ion-exchange bath is conducted for less than or equal to 20 minutes.
 6. The method according to claim 1, wherein ion-exchanging the glass article with the compressive stress greater than 250 MPa in the second ion-exchange bath is conducted for less than or equal to 10 minutes.
 7. The method according to claim 1, wherein the glass article comprises a composition selected from a group consisting of soda lime glass, alkali aluminosilicate glass and alkali aluminoborosilicate glass.
 8. The method according to claim 7, wherein the provided glass article exhibits a composition selected from a group consisting of: (a) 60-70 mol % SiO₂; 6-14 mol % Al₂O₃; 0-15 mol % B₂O₃; 0-20 mol % Na₂O; 0-10 mol % K₂O; 0-8 mol % MgO; 0-10 mol % CaO; 0-5 mol % ZrO₂; 0-1 mol % SnO₂; 0-1 mol % CeO₂; less than 50 ppm As₂O₃; and less than 50 ppm Sb₂O₃; wherein 12 mol %≦Na₂O+K₂O≦20 mol % and 0 mol %≦MgO+CaO≦10 mol %; and (b) 64 mol %≦SiO₂≦68 mol %; 12 mol %≦Na₂O≦16 mol %; 8 mol %≦Al₂O₃≦12 mol %; 0 mol %≦B₂O₃≦3 mol %; 2 mol %≦K₂O≦5 mol %; 4 mol %≦MgO≦6 mol %; and 0 mol %≦CaO≦5 mol %, and wherein 66 mol %≦SiO₂+B₂O₃+CaO≦69 mol %; Na₂O+K₂O+B₂O₃+MgO+CaO+SrO≧10 mol %; 5 mol %≦MgO+CaO+SrO≦8 mol %; (Na₂O+B₂O₃)−Al₂O₃≦2 mol %; 2 mol %≦Na₂O−Al₂O₃≦6 mol %; and 4 mol %≦(Na₂O+K₂O)−Al₂O₃≦10 mol %; (c) 61 mol %≦SiO₂≦75 mol %; 9 mol %≦Na₂O≦21 mol %; 7 mol %≦Al₂O₃≦15 mol %; 0 mol %≦B₂O₃≦12 mol %; 0 mol %≦K₂O≦4 mol %; 0 mol %≦MgO≦7 mol %; and 0 mol %≦CaO≦mol %; (d) 50 mol %≦SiO₂≦70 mol %; 8 mol %≦Na₂O≦16 mol %; 9 mol %≦Al₂O₃≦17 mol %; 2 mol %≦B₂O₃≦12 mol %; 0 mol %≦K₂O≦4 mol %; 0 mol %≦MgO≦4 mol %; and 0 mol %≦CaO≦0.2 mol %, wherein the alkali metal oxides and the alkaline earth metal oxides are modifiers and the ratio: [(mol % Al₂O₃+mol % B₂O₃)÷Σ mol % modifiers] is greater than 1; and (e) SiO₂>50 mol %; 11 mol %≦Na₂O≦25 mol %; 7 mol %≦Al₂O₃≦26 mol %; o mol %≦B₂O₃≦9 mol %; 0 mol %≦K₂O≦2.5 mol %; 0 mol %≦MgO≦8.5 mol %; and 0 mol %≦CaO≦1.52 mol %.
 9. The method according to claim 1, further comprising: applying a low surface energy coating to the first surface of the glass article, the low surface energy coating being selected from the group consisting of fluoroalkylsilanes, perfluoropolyether alkoxy silanes, perfluoroalkyl alkoxy silanes, fluoroalkylsilane-(non-fluoroalkylsilane) copolymers, and mixtures of fluoroalkylsilanes and hydrophilic silanes; and curing the low surface energy coating to form a Si—O bond between the low surface energy coating and the first surface of the glass article; wherein the low surface energy coating has a thickness in the range of 0.5 nm to 20 nm.
 10. The method according to claim 9, wherein the low surface energy coating is a perfluoroalkyl alkoxy silane of formula (R_(F1))_(x)—Si(OR)_(4-x), where x=1 or 2, R_(F1) moiety is a perfluoroalkyl group having a carbon chain length in the range of 16-30 carbon atoms and OR is acetoxy, —OCH₃ or OCH₂H₃.
 11. The method according to claim 9, wherein the low surface energy coating is a perfluoropolyether alkoxy silane of formula [CF₃—(CF₂CF₂O)_(a)]_(x)—Si(OR)_(4-x) where a is in the range of 5-10, x=1, and OR is acetoxy, —OCH₃ or OCH₂H₃, and further wherein a total perfluoroether chain is defined from the silicon atom in the alkoxy silane to the end of the alkoxy silane having a length in the range of 1 nm to 10 nm.
 12. The method according to claim 9, wherein the low surface energy coating is a perfluoroalkyl alkyl alkoxy silane of formula [R_(F2)—(CH₂)_(b)]_(x)—Si(OR)_(4-x) where R_(F2) is a perfluoroalkyl group having a carbon chain length in the range of 10-16 carbon atoms, b is in the range of 14-20, x=2 or 3 and OR is acetoxy, —OCH₃ or OCH₂H₃.
 13. The method according to claim 9, wherein applying the low surface energy coating comprises applying said low surface energy coating to form coating domains and a non-coating domain area on the first surface of the glass article.
 14. The method according to claim 9, wherein applying the low surface energy coating comprises applying said low surface energy coating uniformly across the first surface of the glass article, and further wherein the low surface energy coating has a thickness in the range of 0.5 nm to 10 nm.
 15. The method according to claim 9, wherein the low surface energy coating has a thickness in the range of 1 nm to 3 nm. 